Container refrigeration apparatuses including a refrigerant circuit performing a refrigeration cycle have been used to cool air in a container for use in, e.g., marine transportation (see, e.g., Patent Document 1). The container is loaded with plants such as bananas and avocados, for example. Plants breathe by absorbing oxygen in the air and releasing carbon dioxide even after they have been harvested. The plants lose their nourishment and moisture as they breathe. Thus, the degree of freshness of the plants decreases. Thus, the oxygen concentration in the container is preferably lowered not to cause breathing problems.
Patent Document 1 discloses an inside air control system. In this inside air control system, an adsorbent which adsorbs a nitrogen component in the air when pressurized is used to produce nitrogen-enriched air having a lower oxygen concentration and a higher nitrogen concentration than the air, and this nitrogen-enriched air is supplied into the container to reduce the oxygen concentration of the air in the container, making it easier to keep the plants fresh. This inside air control system performs an adsorption operation of sending pressurized air using an air pump into an adsorption column housing the adsorbent to allow the adsorbent to adsorb the nitrogen component, and then performs a desorption operation of sucking the air using the air pump from the adsorption column to allow the adsorbent to desorb the nitrogen component adsorbed. As a result, the nitrogen-enriched air is produced.